After pouring over 20 years worth of satellite data in an attempt to reconcile different measurements of the polar ice caps, an international team of scientists has compiled the most definitive evidence yet that the polar ice caps are melting at an accelerated rate and contributing to sea level rise.
"Our new estimates are the most reliable to date and provide the clearest evidence yet of polar ice sheet losses," said study leader Dr. Andrew Shepherd, a Professor of Earth Observation at the University of Leeds in the U.K., according to CBC News. "They also end 20 years of uncertainty regarding changes to the Greenland and Antarctic ice sheets. They are intended to be the benchmark data set for climate scientists from now on."
The project, called the Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE), is a joint effort by NASA and the European Space Agency (ESA) which brings together 47 climate researchers from 26 different institutes — including Glenn Milne, a geophysicist with the University of Ottawa's Earth System Dynamics Group — to resolve years of disagreements between various ice-sheet measurements and measurement techniques.
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Combining the 20 years of accumulated data from 10 different satellites — including Canada's RADARSAT-1 mission — and ensuring that the data was all applied over the same geographic area, using the same time spans, and using the same models for surface melting of glaciers and for the rise of land-mass due to glacial melting (known as post-glacial rebound), the team found that the ice sheets of Greenland and Antarctic have been losing mass at an accelerated rate since the early '90s.
Since 1992, the Greenland ice sheet has suffered a loss of between 93 and 191 billion tonnes of ice per year, the West Antarctic ice sheet has lost between 39 and 91 billion tonnes of ice per year, and the Antarctic Peninsula has lost between 6 and 34 billion tonnes of ice per year.
The only ice sheet that has seen some increases is the East Antarctic ice sheet. This is due to climate change causing more snow to fall in that region, but the changes there have still ranged between a loss of 29 billion tonnes of ice per year to a gain of 57 billion tonnes per year. Even with the gains, they are not significant enough to offset the losses from the rest of the Antarctic, and definitely not enough to make up for the losses from Greenland. This overall loss of ice mass is contributing to rise in ocean levels.
"When combined, the full record of satellite data shows that the Antarctic and Greenland ice sheets have contributed just over 11 millimetres to global sea levels since 1992," said Shepherd. "This amounts to one-fifth of all sea level rise over the same period."
Just over 1 centimetre doesn't seem like a lot, but that increase is spread out over the 360 million square kilometers of the surface of our oceans, which adds up to a large volume (and thus a large mass) of water.
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"When you have 11 millimetres of increased sea level, if you compute the amount of mass that's capable of coming onshore during a storm surge, that's a lot of mass," said study co-author Dr. Erik Ivins, who studies glacial isostatic adjustment and sea level change at NASA's Jet Propulsion Laboratory. "And small changes in sea levels in certain places mean very big changes in the kind of protection of infrastructure that you need to have in place."
There are several regions of Canada that would be greatly impacted by sea-level rise. In Atlantic Canada this includes the entire east coast of Nova Scotia from Yarmouth to Louisbourg, the regions of Fortune Bay and Stephenville on the Island of Newfoundland, all of Prince Edward Island, and the north coast of New Brunswick, especially the area around Moncton. Areas along the St. Lawrence Seaway are also at risk, especially those near Sept-Îles and Baie-Comeau in Quebec. On the west coast, the islands of Haida Gwaii (formerly the Queen Charlotte Islands) are especially vulnerable, as is much of the coast of Vancouver Island and the entire city of Vancouver. All of these areas are considered at high risk for devastating storm surges, and this risk will only increase as sea levels rise.
The study, entitled A Reconciled Estimate of Ice-Sheet Mass Balance, was published today in the journal Science, and will be added to the next update to the United Nations Intergovernmental Panel on Climate Change (IPCC) report in 2014.